Despite being publicly listed on US exchanges, a sizable portion of the revenues generated by the companies in the S&P 500 are earned abroad because of their global, interconnected customer base.

The biggest public companies in America now make 41% of their revenue from outside the country. Compared to small-cap companies in the Russell 2000, this is almost twice as much. Businesses that go global have greater access to markets, but they also run the risk of currency fluctuations.

Below graph shows the share of US and foreign revenue across major stock indexes. Data from Citi Global Wealth Investments.

As we can see, the Russell 2000 index, which gives us a picture of small-cap companies in the US economy, generates the majority of sales domestically.

The industries with the greatest exposure to foreign revenue are those in technology and materials; the S&P 500 index also reflects this trend.

Examining the equal-weighted S&P 500 index, we observe that the proportion of overseas sales increases to 31%.

This index gives each company an equal weight of 0.2% of the total, rather than distorting numbers based on the market capitalization of individual companies. 

Furthermore, because the largest companies typically have a higher share of sales driven internationally, this figure increases for the market-cap weighted regular S&P 500. Moderna and Intel, for instance, receive more than 70% of their revenue from outside.